An electric compressor inverter that drives an electric compressor used in vehicular air conditioning equipment includes an input current detection circuit. After a voltage between both ends of a shunt resistor produced as a result of a flow of an input current through the shunt resistor is amplified by an op-amp circuit, this input current detection circuit performs analog/digital (A/D) conversion in a central processing unit (CPU) and detects the input current of the inverter. The input current detected by the input current detection circuit is multiplied by the input voltage to obtain the power consumption of the electric compressor.
In the automobile industry in recent years, fuel-efficient driving has been in demand and, in order to accurately detect the power consumption of an electric compressor that achieves fuel-efficient driving, the accuracy requirements for detecting the inverter input current have become increasingly stringent.
Patent Document 1 described below discloses a motor control device that includes a first op-amp that amplifies an electric potential difference between both ends of a shunt resistor and outputs the difference to a CPU, and a second op-amp that detects an offset voltage. The motor control device corrects a motor load current value computed on the basis of the output of the first op-amp, which changes with the passage of time.